Continuing last column’s spotlight on Minnesota geography (“Minnesota rocks”), we’ll look at architecture built from stone quarried right here in the state. If you missed part one, a brief synopsis of how our diverse geologic landscape was formed can be found here.
But before we get to the actual buildings, do you remember the three basic rock classifications? They’re igneous, sedimentary and metamorphic. Knowing how rocks were formed helps you spot them.
All three of these rock types have been quarried in Minnesota, and many are still cut from the ground today. It’s fun to spot the rocks as you travel through towns across the state and even the country.
If a Minnesota building with stone on it was built before the 1960s, there’s a pretty good chance the stone was from Minnesota. A couple big exceptions to this are the Minnesota State Capitol (that’s our granite on the lower part, but most is Georgia marble) and the Basilica of St. Mary (the granite foundation is from Minnesota but the rest is from Vermont).
Below are definitions of the three rock classifications and a few buildings where you can see them.
Three quarters of the earth’s crust is made of cooled lava from volcanoes. Basalt, the common gray rock found on the ground all over the place, is igneous. So is granite.
Granite: Varies in color from light gray to red to black with small or large grains. It’s still a large industry near St. Cloud, but in the early 1900s there were more than 50 granite quarries throughout the state. Granite can be less rough or polished to a glossy finish.
- Minneapolis City Hall (rough-cut granite from Ortonville)
- Hennepin County Government Center (smooth-cut granite from Ortonville)
- Marquette Plaza
- Plymouth Congregational Church
- I-35W Bridge Memorial
- Lakewood Cemetery’s new mausoleum
- Target Field
- St. Paul Cathedral
Basalt: Not typically used as a building stone, but the old Fitger’s brewery in Duluth is a rustic, fort-like building made of basalt.
Layers of sediment, minerals, plants or shells got cemented together over time under pressure and under water. Think of the colored sandstone layers along Minnehaha Creek near the Mississippi River. Brownstone and limestone are sedimentary rocks. They are too fragile to take a high polish and are usually left in rough blocks or in slabs with a matte finish.
Platteville limestone: Quarried on Nicollet Island and nearby riverbanks. Look for a crumbly looking stone often used for house foundations.
- Pillsbury A Mill
- Nicollet Island Inn
- Grain Belt Brewery’s first floor
- Parts of the Stone Arch Bridge
Kasota limestone: Quarried in Mankato, cut into rough blocks or smooth slabs. Its cream-colored matte nish is very distinctive.
- Minneapolis Post Office
- Uptown theater
- Minneapolis Central Library
- CenturyLink Building
- Stone Arch Bridge
- First Baptist Church
- WCCO-TV Building
- University of St. Thomas, Minneapolis campus
- Wells Fargo Center
- The Westin Minneapolis (Farmers and Mechanics Savings Bank)
As continents collided and other events changed the planet, rocks that already existed sometimes went through tumultuous changes. Metamorphic rocks were transformed by heat or pressure and are completely changed into a different rock type.
Quartzite: Sandstone that has changed into a harder rock. Quarried in southwestern Minnesota.
- Historic Wesley Center (Wesley United Methodist Church)
- Scottish Rite Temple
Morton Gneiss (pronounced “nice”): Look for the swirling red and black polished slabs often found on Art Deco buildings. Quarried in the southwestern town of Morton, Morton Gneiss is immediately recognizable on buildings across the country, especially in Chicago and New York where it was very fashionable in the 1920 and ’30s. Considered one of the oldest rocks in the world!
- CenturyLink Building
- The Baker Building
- Minneapolis Public Service Center
Enjoy an architectural stone exhibit at S. 5th St. and 3rd Ave. from the skyway level food court in USBank Plaza (200 S. 6th St.).